On October 6, the National Institute of Statistics and Economic Studies (Insee) published a blog post describing a study conducted with the Data and Statistical Studies Service (SDES) of the Ministry of Ecological Transition. The study examined the real-world impact of insulating individual homes using communicating meters, specifically Linky for electricity and Gazpar for gas. The findings show that the actual energy savings achieved are only 42 percent of what was predicted in theoretical models. The SDES used anonymized monthly records of about one million households, dating back to 2018, to conduct the evaluation. The study focuses on homes heated by electricity or gas, with the SDES noting that 61 percent of homes renovated with support between 2020 and 2023 were owner-occupied. These homes made up 92 percent of beneficiaries of the MaPrimeRénov' program, which supports renovations involving a single type of work. The study only includes households that completed one wave of subsidized insulation, such as on windows, walls, attics, floors, or roofs, while excluding those who also changed their heating systems. The researchers emphasize that their findings do not apply to major renovations. To assess the effect of insulation, the study compared two consumption patterns: homes that underwent renovations and similar homes that did not receive subsidized work. This control group helps account for factors like milder winters or changes in energy prices. Starting in 2022, rising energy costs led many households to reduce consumption, but the researchers believe this effect is limited. They used the Tremi survey, which focuses on energy renovation in individual homes, to cross-reference their data with support programs. Conducted by the Agency for Ecological Transition (Ademe) and the SDES, this survey helped identify homes renovated without subsidies. The researchers estimate that about 700,000 homes were renovated without support in 2019, representing nearly 3.5 percent of all homes. Although heating methods were not recorded, they were estimated using a statistical model that accurately predicted the method in more than nine out of ten cases. The study covers work completed between 2018 and 2024. For homes heated by electricity, average electricity consumption decreased by 5.0 percent, saving 0.5 megawatt-hours (MWh) per year compared to the 1.2 MWh of theoretical savings. For gas-heated homes, the decrease was 6.6 percent, or 0.8 MWh per year compared to the expected 1.9 MWh. The researchers note that a third of electricity use is for purposes other than heating, such as lighting. These results are slightly lower than those from a first version of the study released in July 2025, but the gap between actual and theoretical gains remains the same. The revision was due to better identification of households and a longer study period. In terms of cost savings, insulation allows electricity-heated households to save an average of 106 euros per year, while gas-heated homes save about 95 euros annually. However, the cost of the work is known for only 20 percent of the renovating households in the study—those who benefited from MaPrimeRénov' or the tax credit for energy transition (CITE). For these households, the average cost of insulation before subsidies was 11,700 euros for electric heating and 12,900 euros for gas. After subsidies, the remaining cost was 7,200 euros and 7,900 euros, respectively. In this subgroup, annual savings on the bill reached 90 euros for electricity and 160 euros for gas. Other financial supports, such as energy savings certificates (CEE), may be added, but these are not included in the data. The researchers note that the gap between theoretical and actual savings is well-documented in economic studies. A 2023 American study found that 43 percent of the gap could be attributed to poor work quality, while overly optimistic assumptions in models explained 41 percent. The "rebound effect," where households use more energy due to lower costs, accounted for only 6 percent. On French data, no increase in energy use was observed even four years after the work. The researchers also highlight that insulation aims to improve comfort and reduce energy poverty, which affected 3.1 million households in 2023. According to the Tremi survey, 70 percent of homeowners who renovated between 2016 and 2019 reported improved comfort.